Victron Smart Shunt - 500A version enough?

MagicalArmchair · 1 Mar 2024

Evening all, the cable on Mirage is 95mm battery cable, which is rated to 500A, so I presume the 500A version of the SmartShunt will be enough? I won't need the bigger 1,000A version?

Victron Smart Shunt 500A/50mV

The most meaty thing I have that takes draw is my windlass, that apparently draws 150A under load (Horizontal Windlass - Cayman).

PaulRainbow · 1 Mar 2024

MagicalArmchair said:
Evening all, the cable on Mirage is 95mm battery cable, which is rated to 500A, so I presume the 500A version of the SmartShunt will be enough? I won't need the bigger 1,000A version?

Victron Smart Shunt 500A/50mV

The most meaty thing I have that takes draw is my windlass, that apparently draws 150A under load (Horizontal Windlass - Cayman).

The size of your battery cables is irrelevant, it' the max load that counts. So if your windlass, at 150a is the biggest current draw the 500a Smart Shunt will be fine.

Buck Turgidson · 1 Mar 2024

I'm sure 500A is enough for most boats but I think you should calculate the maximum total load rather than just the single highest. I'm thinking of that day when you need to start the engine while the windlass is stating. I know it's extremely unlikely but not impossible.

Tranona · 1 Mar 2024

Buck Turgidson said:
I'm sure 500A is enough for most boats but I think you should calculate the maximum total load rather than just the single highest. I'm thinking of that day when you need to start the engine while the windlass is stating. I know it's extremely unlikely but not impossible.

Surely not an issue if the engine has a dedicated battery as the shunt will be on the domestic bank.

Buck Turgidson · 1 Mar 2024

Tranona said:
Surely not an issue if the engine has a dedicated battery as the shunt will be on the domestic bank.

True enough if the batteries definitely split during engine start but this may not always be the case. My point was to check the maximum total theoretical load just as you would for cable.
I’ve got a video of my house battery discharging during engine start as the voltage doesn’t drop enough to trigger the VSR

MagicalArmchair · 2 Mar 2024

Thank you all for the responses. The house and starter banks are isolated from one another, so it should be fine. That is good news I don’t need the 1,000A version! Far cheaper!

KompetentKrew · 2 Mar 2024

500A @12V would be 6kW - running two electric kettles at he same time. Or an electric kettle, an immersion heater and your windlass.

You'd need quite a big old bank of batteries to handle that load.

Neeves · 2 Mar 2024

MagicalArmchair said:
Thank you all for the responses. The house and starter banks are isolated from one another, so it should be fine. That is good news I don’t need the 1,000A version! Far cheaper!

I wonder what the smallest shunt would be for your application - you might be able to save more. Nothing wrong with over specifying (I assume) except there might be a cheaper option and still be technically acceptable.

Some slight drift

We would always already have an engine (or both engines) running prior to using the windlass, they help to ensure you are in the best desired location, reduce the drain on the battery(s) when you use the windlass (and heat the water ready for that welcome how shower.). I know the purists would scoff (and sail to their anchorage but they possibly don't favour hot showers, nor grandaughters and recommend hair shirts).

Jonathan

vas · 2 Mar 2024

I hope you are aware of the function of the shunt.
I do have a 500A Victron shunt and on my lifepo4 bank a 200A one needed by the diyBMS. Boat is 24V though.
Victron even with inverter in full blast, watermaker et al running, wont even go north of 120-130A

But anyway, what's going to happen? Doubt your batteries are going to be strong enough to reach 500A (let alone push above it), but assuming they do, they'll just record 500A whereas it's going to be say 520-550A for a few secs (if at all), so what? you will get a missreported load... I'd be more worried that you have a system capable of drawing 500A for any meaningful amount of time

EDIT: not to mention that if you want accuracy in reported Ah, you better get a shunt close to your maximum anticipated current load and not on the max theoretical current the battery cable may sustain.

simonfraser · 2 Mar 2024

had a 500Ah victron shunt that started my KAD 42 no probs

justanothersailboat · 2 Mar 2024

How big's the main fuse?

Not much point in having a shunt vastly higher rated than that... a bit higher yes, lots no.

there seems to be quite a lot of variation in boats' sophistication and loads, but 95 sq mm main battery cable is big stuff and suggests a hefty system.

PaulRainbow · 2 Mar 2024

justanothersailboat said:
How big's the main fuse?

Not much point in having a shunt vastly higher rated than that... a bit higher yes, lots no.

there seems to be quite a lot of variation in boats' sophistication and loads, but 95 sq mm main battery cable is big stuff and suggests a hefty system.

Not necessarily, some production boats are built with standard wiring harnesses, the main battery cables are at least as big as would be needed if every possible option was specified, whereas in reality the boat may have minimal options.

PaulRainbow · 2 Mar 2024

Buck Turgidson said:
True enough if the batteries definitely split during engine start but this may not always be the case. My point was to check the maximum total theoretical load just as you would for cable.
I’ve got a video of my house battery discharging during engine start as the voltage doesn’t drop enough to trigger the VSR

The most the engine can possibly draw from the domestic batteries is the rating of the fuse for the VSR. What's that, 120a ?

120a for the engine, 150a for the windlass, everything else on the boat turned on at one, 20a (must be lots of gear onboard), so a total of 290a, well in spec for a 500a shunt.

Plum · 2 Mar 2024

MagicalArmchair said:
Evening all, the cable on Mirage is 95mm battery cable, which is rated to 500A, so I presume the 500A version of the SmartShunt will be enough? I won't need the bigger 1,000A version?

Victron Smart Shunt 500A/50mV

The most meaty thing I have that takes draw is my windlass, that apparently draws 150A under load (Horizontal Windlass - Cayman).

I asked Victron if their 500A shunt was capable of taking my starter motor current. I asked "...... the largest load I will ever put through it will be for my starter motor rated at 3000W so even if the voltage remained at 12v during cranking and allowing X2 for peak should a 500A shunt be OK? However, my battery has a CCA of 1000A but if the starter motor is only going to draw a max of 500A, is a 500A shunt still OK?"

The reply from Victron was "Yes for those calculations 500A is sufficient"

Victron Smart Shunt - 500A version enough?

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